Conventional binders to bind sand grains to each other include many inorganic based or organic based binders. Typically, a mold that is composed of solidified sand grains with such a binder is used as a core mold. Such a core mold is disposed in a casting cavity to cast an article such that the core mold forms a contoured surface that is contoured to the inner surface of the cast article. One example of the conventional binders is a phenol-formaldehyde resin.
As one conventional molding process, a shell mold process is known as disclosed in Japanese Patent Early-Publication No. 10-193033. The shell mold process is to use molding sand that is coated with the binder, and to charge it into a heated metal mold using a blowing introducing process. The coating binder of the charged molding sand is then cured by the heat transferred from the mold.
Another conventional molding process uses a water-soluble binder as disclosed in Japanese Patent Early-Publication No. 55-8328. This process is to freeze a mixture comprising the water-soluble binder, water, and molding sand, while the mixture is kneaded.
The frozen mixture is charged into a pre-heated mold using a blowing introducing process. The charged mixture is then dried and thus cured.
The forgoing process disclosed in Japanese Patent Early-Publication No. 10-193033 involves the binder generating volatile gases, such as a formaldehyde gas, a phenol gas, and an ammonium gas, while the binder is thermally cured by the heat transferred from the metal mold. The volatile gases involve unpleasant odors or impose biohazards for a human.
A core mold to be assembled to form a mold often contains a binder that is based on a urea-phenol-formaldehyde resin or a phenol-formaldehyde resin. Pouring a molten metal of an iron alloy or a light-metal alloy into such an assembled mold heats the binder, and in turn it is volatized or decomposed to generate gas, which may cause voids to form within the poured molten metal.
The typical use of the core mold with a resin-binder for casting a non-iron alloy, e.g., an aluminum alloy, resulted in the resin-binder being insufficiently volatized or decomposed, since the temperature of the molten metal to be poured into the mold is about 700° C. This may prevent the core mold from being readily removed from the cooled and solidified molten metal. The insufficiently removed core mold needs to be shaken, or to be re-heated so that the solidified molten metal in turn volatizes or decomposes the binder, in order to remove it.
The forgoing molding process disclosed in Japanese Patent Early-Publication No. 55-8328 is to freeze the mixture of the water-soluble binder, the water, and the molding sand, as noted above. This results in silica sand grains within a blow-head being concentrated to be formed as rocks or clots when the frozen mixture is charged into the metal mold. This effect is also possible in the interval between two adjacent cycles of charging. This effect involves the difficulty in continuously charging the mixture from the blow-head into the mold. Indeed, such a molding process has not yet been practiced.
When the core mold with the water-soluble binder is deposed in a high-humidity environment, the water-soluble binder typically absorbs water and thus its binding force is weakened, to cause the deformation of the core mold. As a result, the core mold may not maintain its shape. Even such a core mold can be used in the molding process, and the moisture within it is heated and vaporized when the molten metal is poured into the core mold. The resulting vapors form voids within the poured molten metal.